Generic drive mechanisms are specially used for mobile machines such as wheel loaders, graders, or excavators. In wheel loaders, particularly wheel loaders greater than 12 tons, the whole driving range is divided in two driving ranges, one working range, preferably up to a speed of about 20 km/h, and one transport range which can extend to a speed of up to about 40 km/h. In the course of the working range it is advantageous if the whole speed range can be achieved without mechanical gear shifts since, through each mechanical gear shift, due to the change of ratio, the time required increases the working time of the wheel loader.
EP 0 483 543 B1 has disclosed a hydrostatic drive mechanism, preferably a ground leveling device, such as a wheel loader, in which a first axial piston hydromotor and a second axial-piston hydromotor are shifted together in one summarizing gear in a manner such that in a starting gear the torques of both hydromotors drive the output shaft and, in a final speed, one hydromotor is in idling speed and the other hydromotor alone drives the input shaft. Between the starting and the final speed, several ratio steps are shifted, preferably via synchronizer units. Disengaged at the final speed, the motor is at zero absorption volume and in idling speed, since said motor would otherwise overspeed. The synchronizer units have to synchronize both the drag torque of the gear wheels and the drag torque of the whole axial piston motor with the pistons and cylinders thereof. Since the motor is also pressurized at zero absorption volume, the bearings of the output shaft of the hydromotor undergo considerable axial forces which increase the synchronizing torque. To achieve a final speed of almost 40 km/h, the drive mechanism needs two hydromotors and at least two shift devices whereby a gear shift cannot be prevented in the working range.
The problem on which the instant invention is based is to provide a drive mechanism for a mobile vehicle, specially of a mobile machine such as a wheel loader, which stands out by simple construction of the reduction gear, the same as by as few as possible gear shifts in the working range.